There have hitherto been known certain hydraulic cylinder devices of the type described as disclosed, for example, in Japanese Unexamined Utility Model Publication No. Hei 6-39285 and Japanese Unexamined Patent Publication No. Hei 6-155089, in the prior art.
There is disclosed in the former publication above a hydraulic cylinder device or apparatus which, as shown in FIG. 1 of the drawings attached hereto, makes use of a high speed cylinder a that has a smaller pressure receiving area and a pressurizing cylinder b that has a larger pressure receiving area, the two cylinders being arranged coaxially and vertically up and down. The two cylinders a and b have their respective pistons c and d interconnected by a piston rod e and are assembled providing a so-called double rod cylinder configuration in which the upper end portion of the piston rod e is allowed to protrude upwards of the high speed cylinder a.
In the apparatus so constructed, it may be noted that via pipes and valves arranged externally of the two cylinder assembly, a pressure fluid is supplied to the high speed cylinder a to cause the pistons c and d to act rapidly and thereafter is supplied to the pressurizing cylinder b to develop an increased pressing force, thereby meeting with a requirement for a greater or higher load.
It may also be noted that the latter publication above discloses a hydraulic cylinder assembly which, in addition to having a basic construction that is essentially the same as the assembly described, as shown in FIG. 2 of the drawings attached hereto, has an interconnecting rod e that is provided, where the rod joins with the piston d in the pressurizing cylinder b, with a sequence valve f that can be opened and closed by a pilot pressure and used to switch the operation from a high speed into a high pressure mode. With the cylinder assembly so constructed, the apparatus is rendered capable of meeting with the requirements for a high speed (rapid) and a high load (heavy) operation without requiring the above mentioned pipes and valves as arranged externally of the cylinder assembly.
Despite these advantages, however, the prior devices have been found to be much unsatisfactory and inconvenient. Thus, the first mentioned known cylinder apparatus has been found defective in providing a satisfactory "detachment" force and therefore inconvenient, for example, when used as a drive source in a press with a pressing (upper) die and a receiving (lower) die where the latter die may have been caused to "bite" the former die in a pressing operation, because it may be rendered unable to detach the die (upper) that was bit from the die (lower) that bit.
It has also been noted that the second mentioned known cylinder apparatus in which a sequence valve f is provided internally where the piston rod e joins with the piston d in the pressurizing cylinder b is found defective and inconvenient because of its poor outfitting capability.
It should further be noted that neither of these assemblies in which the double rod cylinder configuration is adopted for the upper cylinder as well requiring the entire assembly to be lengthened, would be satisfactory or convenient if adapted, for example, in a press because the press would then have to be sized to be greater in height and larger.
Yet, it should be noted that both the arrangements are not economical or convenient because of the requirement that a single rod e serve commonly as both the piston rod for the high speed cylinder a and the piston rod for the pressurizing cylinder b, that is, be hence of a single given for both the cylinders but unnecessarily enlarged diameter for the high speed cylinder.
With the view to eliminating such inconveniences and deficiencies as encountered in the prior art, it is an object of the present invention to provide a high speed and high load operable hydraulic drive cylinder system which makes it easier to detach a die "that has been bit" from a die "that has bit" as mentioned above, allows a press or the like machine tool for use therewith to be considerably smaller sized and is rendered economical. It is another object of the present invention is to provide a method of controlledly operating a system as described.